1. Field of the Invention
The present invention relates to a method for manufacturing a filter element having a number of concavities and convexities on an outer peripheral surface thereof by suction molding, and a molding die for use therein.
2. Description of Related Art
It is proposed in U.S. Pat. No. 5,755,963 (EP 0755710 A1) to manufacture by suction molding a filter element having a plurality of fin-like portions formed on an outer peripheral surface thereof. In this method, as illustrated in FIGS. 11 and 12, there is used as a molding die a suction jig 50 that is composed of a protector 51 having a number of suction openings 51a formed therein and defining an inner peripheral configuration of a molded body 60 and a contouring jig 52 defining an outer peripheral configuration of the molded body 60, whereby a slurry containing therein fibers used as filter material is sucked and molded via a suction core 53 assembled to the inside of the protector 51 to thereby form the molded body 60. The contouring jig 52 has a plurality of leg portions 52a disposed in such a way as to oppose the concavities of the protector 51 and gaps permitting the passage of the fibers therethrough are formed between these leg portions 52a. By causing the slurry containing the fibers therein to flow in from between the leg portions 52a and thereby causing the fibers to be accumulated there is suction molded the molded body 60 having a plurality of fin-like portions formed on the outer peripheral surface thereof.
However, in the case of this manufacturing method, there remains a likelihood that when the slurry containing fibers therein is sucked via the protector 51 and flowed in from between the leg portions 52a, the fibers contained in the slurry might be caught between the leg portions 52a and the protector 51, especially, in the vicinity of forward end portions 52b of the leg portions 52a, whereupon the fibers contained in the slurry sequentially sucked are hindered from flowing toward the protector 51 by the fibers which has thus been caught. As a result, it is likely that, as illustrated in FIG. 12, non-walled portions 54 may be formed in part of the molded body 60.